1. Technical Field
This application relates to an adjustable hydrocephalus valve to equalize the pressure of the liquor in the cranium of a hydrocephalus patient.
2. Background Information
Hydrocephalus patients have the following medical problem: The brain is surrounded by a special liquid called liquor. This liquor is continuously being produced and reabsorbed in equal amounts. In the illness hydrocephalus (also called water on the brain), this equilibrium is disrupted and more liquid is produced than is reabsorbed. Because the interior of the skull represents a closed vessel, the result is an increase in volume. In infants, the seams in the skull cannot grow together and close, and in adults the internal pressure in the skull increases. Therefore there are two varieties of hydrocephalus: adult and infantile.
Hydrocephalus treatment initially consisted of simply draining the liquor. This drainage was effected by means of a simple hose connection between the skull and a large blood venous blood vessel or by a corresponding connection between the skull and the abdomen via a hose. It was quickly determined, however, that the pressure in the skull must maintain a certain physiological value if other complications are to be prevented.
In the treatment of hydrocephalus, implantable drains are used to create an artificial connection between the ventricles of the brain in the head and a drainage compartment, which is currently most often the abdomen.
A number of different types of valves are known that are installed in the drain for the liquor, and by means of which the pressure of the liquor can be set. Valves of this type are implanted under the skin in the vicinity of the head. The valves are designed to open at a certain critical pressure and to release the flow of liquor. By means of a line—which is also implanted under the skin—the liquor is drained into the upper vena cava or into the abdominal cavity.
The valves of the prior art help considerably, of course, but a satisfactory solution has not yet been achieved with the valves of the prior art.
For example, valve developments are disclosed in the prior art that make possible a percutaneous, non-invasive adjustment of the opening pressure.
The valves in question are implanted in the patient and preferably drain the excess liquor from the patient's skull via a hose, which is likewise implanted, and empty into the vena cava or into the abdomen. The valve pressure is thereby determined by a spring, whereby the spring is adjusted by means of a mechanism that has a pivoting or rotating part that is moved from outside by pivoting or rotating an integrated magnet, so that the tension on the spring is increased or relaxed.
The valves of the prior art have a more or less flat construction. The objective of the flat construction is to prevent bumps or protuberances on the patient's head to the maximum extent possible as a result of the implant procedure.
The best-known valves include the Codman Medos valve (U.S. Pat. No. 5,928,182).
This valve is a ball valve with a spring-loaded ball. The valve is adjusted by changing the position of the spring. The spring presses with one end on the valve ball. With the other end, the spring is braced against an abutment. In this model, the height of the abutment can be adjusted by rotation. The height can be adjusted because the abutment is rotational and is provided on top with an inclined edge along which the spring glides.
Patent Application EP 1380317 A1 teaches an improvement for this valve, by means of which an unintentional adjustment of the rotor and consequently of the opening pressure can be prevented. In this patent, a clip that is integrated into the silicone jacket is engaged laterally with the rotor, to effect a lateral clamping of the rotor and to prevent the unintentional adjustment of the valve. The function of a construction of this type is somewhat doubtful, however, because in actual use, the housing is carrying a flow of a watery solution (liquor). The sliding characteristics between silicon and the rotor are thereby unfavorably altered. The elastic tension is insufficient to guarantee a friction-tight protection against twisting.
The valves of the prior art also include the Sophysa valve (Patent No. FR 8105389; EP 0060369; U.S. Pat. No. 4,443,214).
Even the manufacturer of this valve warns that the hydrocephalus patient should avoid touching permanent magnets in toys, headsets, loudspeakers and electromagnetic fields of the type that are emitted by electric motors, electric shavers, hair dryers, switches etc. This warning from the manufacturer is tantamount to a warning against being around most of the things people come in contact with in everyday life. Since it is practically impossible for a modern human being to avoid contact with such things, proposed solutions of this type are simply impractical. The manufacturer has recently introduced an improved version of this valve to the market (U.S. Pat. No. 5,643,194). This new model, in fact, does provide some protection against unintentional adjustments. Two radially movable magnets that sit on a rotational rotor are arranged so that they attract without any external action and thereby block the rotor in notches created on the housing. Stronger magnets that are applied externally can then overcome the attractive forces on the valve side and pull the magnets apart radially. As a result, the rotor is unlocked, and by rotating the rotor by rotating the externally applied magnets around the axis of the rotor, it becomes possible to adjust the opening pressure. This principle has in fact shown itself to be susceptible to failure in actual practice. Although unintentional rotation is prevented, the intended adjustment is frequently unsuccessful. This problem can be traced to the difficulty of reliably determining the exact position of the valve, because in actual use, friction forces that are difficult to calculate interfere with or even totally prevent the movement of the sliding magnets inside the valve. An additional disadvantage is that because the layers of skin at these points can be rather thick, the two sliding magnets must be pulled far apart, whereby the forces resulting from the externally applied magnetic field become exponentially smaller as the distance increases, and in any case are then no longer sufficient to pull the magnets apart. A simplification and improvement of this arrangement is necessary and desirable.
The principle of a magnetic clamping of a rotationally mounted rotor, which was disclosed as long ago as U.S. Pat. No. 4,676,772 in 1987, has never established a foothold in the market. Here, too, the extremely problematic technology of a 100% magnetic brake in a hydrocephalus valve also becomes apparent. By means of extremely small magnets that are integrated into a rotational flat disk, on which two pins are oriented parallel to the axis of rotation and are inserted into a threaded portion that contains a ball that can rotate along a thread, the height of the threaded portion can be adjusted, as a result of which the force that is exerted against the ball by a silicone membrane can be reduced or increased. To rotate the adjustment disc, first the attractive force between the magnets integrated into the disc and a ferromagnetically active housing part must be overcome by strong magnets that are applied externally. The disc is thereby lifted up slightly, so that rotation becomes possible. This principle has never been found to be either practical or reliable. In particular, the many small moving parts contribute to a critical addition of disruptive friction forces, which cannot be controlled, for among other reasons on account of the small size of the valve and also as a result of the magnets used. The pins can very easily tip out of alignment, and the friction in the threads that is applied externally with a long lever arm is almost impossible to overcome with the very weak magnetic field derived from the small magnets. The thread must also have some play to allow smooth movement, which in turn is disadvantageous to the accuracy of the adjustment. The location of the valve is also problematic here, and an exact adjustment is practically impossible to achieve on account of the small size of the parts that have to be moved. Because of the use of a silicone membrane, the reproducible setting of the opening pressure is impossible, because the properties of the material vary incalculably. For the reasons indicated above, this design has not yet reached a stage where it is ready for the market.
An additional system is offered by Medtronic/OS-Medical (U.S. Pat. No. 5,637,083). Here too, this system teaches that the opening characteristic of a valve can be manipulated through the skin by the rotation of a rotor into which two magnets are integrated. The patent teaches an unintentional adjustment can be prevented by a mechanical pin that must be deactivated percutaneously. However, clinical use has made it clear that the pin can cause a critical jamming of the rotor. The manufacturer was forced to withdraw this unreliable technology from the market and thereafter market the valve without the mechanism to prevent the unintentional adjustment. The danger of the unintentional adjustment therefore remains present, in particular when the requirement for the ability to reliably adjust the valve is taken into consideration.
An additional disadvantage of the system of the prior art is that the adjustment must be effective both in the standing position as well as in the reclining position. However, this is a characteristic that is frequently undesirable. The setting of a characteristic valve pressure that becomes effective only when the patient is in a standing position is both therapeutically logical and helpful. On account of the hydrostatic pressure differential that occurs only when the patient is in a standing position—in particular with the ventriculo-peritoneal drain—in the systems that have been available up to now, as described above, it is of course possible to counteract the complications that result from excessive drainage caused by an elevation of the opening pressure, although at the same time a desired, appropriate draining of cerebrospinal fluid when the patient is lying down—as could be ensured by a low setting of the opening pressure—is systematically prevented.
The consequence for the patient is a physiologically uncomfortable pressurization of the ventricle of the brain immediately after standing up, which can lead to discomfort and dizziness as well as to serious complications such as subdural effusions and bleeding that must be treated by surgery. It is not possible to prevent such complications with the valves described above. Of course, by turning up the valve, the negative pressure in the standing position can be modified in a positive direction, although simultaneously the increased pressure also acts in the reclining position, where it is altogether inappropriate. The higher setting therefore on one hand reduces the undesired extremely negative pressure in the standing position, but at the same time it prevents a therapeutic effect in the reclining position, in particular when the patient is resting or sleeping.